Background: Acute kidney injury (AKI) is a common adverse drug reaction in cancer patients, but case-reports suggest that it may also be the first symptom of occult cancers and may worsen the prognosis of cancer.

Objectives: To examine the risk and prognosis of cancer following AKI.

Methods: We conducted this nationwide cohort-study in Denmark (population 5.6 million) using population-based medical databases. We identified all patients with hospital-diagnosed AKI between 1995 and 2017. We obtained data on any subsequent incident cancer (except non-melanoma skin cancer) and cancer stage. We quantified the 1-year and 1-5-year risk of cancer after AKI using the cumulative incidence method accounting for death as a competing risk. Standardized incidence ratios (SIRs) were computed as the observed number of cancers during the follow-up time divided by the expected number based on national cancer incidence rates by age, sex and calendar year. We computed five-year survival for patients diagnosed with solid and hematological cancer within one year after AKI using the Kaplan-Meier method and compared this with a cancer comparison cohort matched (1:5) on cancer site, age, sex, and year of cancer diagnosis. The 5-year hazard ratios (HR) of death with 95% confidence interval (95% CI) were computed using Cox regression analysis adjusted for age, sex, calendar year, Charlson Comorbidity Index Score, and cancer stage in solid cancers.

Results: We identified 29,977 patients with AKI. Among these, 1303 were diagnosed with cancer within the first year [1-year risk 4.4% (95% CI: 4.2—4.7) and SIR 4.6 (95% CI: 4.4—4.9)] and 827 were diagnosed with cancer 1-5 years after first AKI diagnosis [1-5 year risk 6.7% (95% CI: 6.3—7.2) and SIR 1.3 (95% CI: 1.2—1.4)]. The 1-year SIRs were highest for multiple myeloma, liver cancer, urological cancers, and cancer of the uterine cervix. The prevalence of distant metastases in solid cancer diagnosed within one year after AKI was similar in patients with and without a previous history of AKI (27% vs. 24%). The 5-year survival was 17% for patients with AKI and solid cancer and 39% in the corresponding comparison cohort (adjusted HR = 2.4, 95% CI: 2.1—2.8). The 5-year survival was 29% for patients with AKI and hematological cancer and 48% in the corresponding comparison cohort (adjusted HR = 2.8, 95% CI: 2.3—3.3).

Conclusions: Hospital-diagnosed AKI appeared to be a marker of occult cancer, but is also associated with an increased cancer rate beyond the first year, and signals a poor prognosis.